Welder control system



e ,fj M 0 l M 6, W,f 2 I6 7 im i M M .W mm Rmm ES., mm Amm @ww .Re 5mm w mw m, u w Y D Patented Dec. 23, 1952 OEFICE y WELDER 'CONTROL SYSTEM Ernest G. YAnger, Wauwatosa, Wis., assigner 'to Square'D Company,` Detroit, Mich.,r a corporation of vMichigan ApplicationDecember 8, 1950, Serial'No. 199,847

(Cl. 2MB- 4) 1o Claims. 1

This inventionrelates to an electronic circuit for controllingfthe passage 'of current toa "Welding load, andfor'eiecting such current flow in syn'- ch-ronism with the application .of pressure tothe welding electrodes'. v

I nfmany industrial welding applications, itis desirable to make successive Welds with great rapidity, and in such 'applications it has been ioundthat as` many as 600 welds per minute can be made, using a '6G cyclesourca for controlling such a welding system inustop'- erateso astc allow currentflow.through .the welding transformer only during those :periods in which the successively operating welding electrodes are pressed upon the work. Inasrnuch as electrode pressure ris effected by pressurized fluid new controlled by an electric "valve, it is clear that .the welding control circuit' `must be designed so as to compensate for the inertial effects of such a pressure system. Itis further necessary'that the welding'control circuit also provide for aninitial squeeze period, which is that period during :which pressure is applied to the welding electrodes before. current flows therethrough, which is longer than subsequent squeeze periods 1in any sequenceof `vvelds so that the necessary weld rapidity'may be effected.

It isan object of .thepresent invention to pro-'- vide'an .improved electronic welding circuit which operates in conjunction witha pressure 'systernfso as to pass current through `the welding loadionly during that period in which substantial pressure is applied to the welding. electrodes.

An object of the present invention is the .pro-

vision of a circuit in accordance with the preceding object .in which Athe initial fsqueeze period in avseries of'welds is .longer Vthan zthose in .sub-

sequent welds in Afthe same series.

It is'y also 'anicbjectto providean v.electronic Welder control Vcircuit in which vthe initiation of theV hold" time period i's'independent of the A circuit` vductors 6., 1,58 and 9.

Other objects and features of the invention will be readily apparent to those skilled in theA art from the speciiication and appended drawing illustrating certain preferred embodiments in which:

The ligure is a diagrammatic representation cfa welding circuit in which the circuit arrangement of the Apresent invention is incorporated.

In the figure, the .numerals I and 2 represent a pair of power supply lines which are connected to a source of energy which is not shown.

Connected across the supply lines is the primary 3 of a transformer d which has a secondary 5 which ,supplies voltage to a plurality of con- Connected between conductors G and l8 are a resistor il, and a rectifier i2', the rectifier l2 serving with a capacitor I3 to supply aD. iC. voltage between conductors 1 and 6. A capacitor. I4 is provided which operates with a rectier l5 to supply a D. C. voltage-be-r tween conductcrs 1 and 9.

Also connected between supply lines l and .2 is the primary IG of a transformer I1 having ya secondary I8 which supplies electricalenergy to primaries 19 and 2| of transformers 22 and 23 respectively. Transformer 22 has a secondary 24 which .is connected between conductor 1 and a'conductor 25. Transformer 23 has a secondary 2B which is connected between conductor 9 and conductor 21.

serially connected between conductors 25 and 9 is a capacitor 28 and a resistor 29; and to :a point between these two elements ,there isk connected a shield grid Si of an electronic tubel 3.2, the fadded. squeeze tube, ,havingV an: anode 33 and a cathode 34, and a control grid '36 ywhich is connected to conductor 21'. The anode 3'3 is connected. through relay contact 31' and "resistor 33 Ato vconductor 8,.

Between conductors 1 .and 9 there is disposed apairfof voltage-dividing resistors 39 yand 4'|,-and to a junction between these resistorsthere is con'.- nected one terminal 'of ya'rheostat 42j, the other terminal of which'is connectedto the :conductor 21throughafcapacitor 43.

To .the conductor 1 there vis connected-one teie minal `of a rectifier lill, lthe other 'terminaltliero'f being connected.l .to another, opposed rechner-45. which is falsozconnected .to aconductor 146 `lwhich. as will be seen from `the figure, is connectedto the'an'ode 33. of itube32fthrou'gh `the relay contact 31. To .this conductoriit therei'sv'connected the cathode A11 of' far-,tube :48, fthe' fsqueae time tube, having ein-.anode 419 andzcontrolaand shield grids 5.1 .andf52 respectively. yThe VIAcontrol--g'rid f5'lflsy electrically connected to a pair of voltage-dividing resistors 53 and 54, which parallel rectifier 44, through a rheostat 55. The resistor 54 is connected to the junction between rectiers 44 and 4'5 and through a normally closed relay contact 56 to control grid 5|. Disposed between cathode 41 and control grid 5| of tube 48 is a capacitor 51. The anode 49 of tube 48 is connected to a conductor 8 through a resistor 58, and the shield grid 52 is connected to conductor 25 through a capacitor 59, a resistor 9| being disposed between the shield grid 52 and the cathode 41.

Electrically connected to the anode 49 is a resistor 89 parallelled by a rectifier 64, an opposed rectifier 65 being connected between rectifier 64 and conductor i'. To conductor 1 there is also connected one terminal of a resistor 86, the opposite terminal of which is connected to a recti fier 81 connected in line 25, the rectifier 6'! serving to pass half wave lpulsations through resistor 66.

:'Serially connected rheostat 68 and capacitor B9 are connected in parallel with rectifier 65, the capacitor 69 being paralleled by a normally closed relay Contact 1 I. To the junction between rheostat 68- and capacitor 89 is connected a secondary winding "12 of a transformer 13, the primary of which is connected across the power supply lines fand-2. To an intermediate point'cn the secondary 12 is connected the cathode 14 of an electronic .weld time tube 15 which has an anode 16 and a control grid 11, the latter element being connected to a point between a pair of voltagedividing resistors 18 and 19 which are disposed between conductors 'I and 9. Connected in parallel withA each other, and in series with the anode 18 of. tube 15 are a pair of primary windings 8| and 82 of transformers 83 and 84 respectively. Transformer 83 has a secondary 85 which is connected to conductor 1, and across which is connected a rectifier 86 and a capacitor 81. In parallel with capacitor 81 is a resistor 88 and a rectifier 89,. resistor 88 also being connected to conductor 9 through a resistor 9 I.

-The rectifier 89 is connected between the control grid 92 and the cathode 93 of an electronic tube 94'which has an anode 95 and a shield grid 95, the latter element being connected to a junction between a resistor 91 and a capacitor 98 which are in series, and are electrically con-v and the anode 49 of tube I 0I and an inductor |02. Amanually operated fno'weld switch |03 is disposed between this circuit and conductor 6. The relay coil 99 controls the closure of a relay contact |04 which is disposed in circuit with the igniters |05 and |06 of electric discharge tubes |01 and |08 respectively, the electric discharge tubes being connected in conventional back-to-back arrangement to main power supply lines I and 2 through the primary of welding transformer |09. Across the secondaryof transformer |09 are connected weldingr electrodes IIO, which are adapted to be pressed against the work in the conventional manner upon energization of an associater valve solenoidto be subsequently described.

A pair.` of voltage-dividing resistors III and II2, are connectedin series, oneterminal of this series circuit being connected to conductor 6,.the other terminalto the anode of tube: 48 through resistor 63, 'Toa'.point intermediateresistorsy I'I 4 and |I2 there is connected a control grid ||3 of an electronic tube I I4, through a rheostat I|5. Tube 4 is the hold time tube and has an anode ||8, a cathode |I1, and a shield grid II8, and connected between the control and screen grid there is disposed the secondary I I9 of transformer 84. Between control grid ||3 and the anode 49 of tube 48 is connected a capacitor I2|. Anode I I6 of tube I|4 is connected to a capacitor |22, which is also connected to conductor 1,

and to the control grid |23 of an electronic off time tube |24 which has an anode |25 and cathode |25, and a shield grid |21. The control grid |23 is connected through a rheostat |28 to an intermediate p oint between a pair of resistors |29 and |3| which are connected between conductors 1 and 8. Between control grid |23 and rheostat |28 is disposed one blade |32 of a double pole, double throw, repeat-nonrepeat switch |33, which has a second blade |34 connected to the shield grid |21. In the drawing, switch |33 is illustrated in the repeat position in which, as shown, shield grid |21 is connected through blade |34 and resistor |35 to conductor 6. Conductor 8 is connected to anode I 25 of tube |24 through a pair of resistors |36 and |31 and a capacitor |38, the anode also being connected to conductor 25 through a relay coil |39. Coil |39 is parallelled by a capacitor |4| which maintains the coil |39 energized during those half cycles' of non-conduction of tube |24 which immediately follow conducting half cycles. The energization of relay coil |39 controls the operation of a relay contact |42, contacts 1I, 56 and 31, and

another relay contact |43 which controls the en-l ergization of a valve solenoid |44 connected be-,g

tween power supply lines I and 2, valve solenoid |44 controlling the application of fluid pressure tothe welding electrodes I|0.

`An initiating contact I 45 is provided across secondary 2| of transformer 23, the relay contact |42 `in parallel therewith insuring the completion of a welding cycle should the initiating contactbe opened at some time during such a cycle.

It should be noted that in the description of y the circuit, certain conventional elements have been eliminated, such as surge bypass capacitors, cathode heaters, a thermal flow switch, etc., although these and other conventional elements would be present in an operating circuit. This..

elimination of conventional parts has been effected for purposes of simplicity, their position andv function being well the art. i

The operation of the system will now be deknown to those'familiar with scribed. Connection of the main power supply` lines I and 2 to a source of electrical energy will eiect the energization of transformers 4, 13 and I1. The secondary 5 of transformer 4 supplies an A. C. voltage between conductors 6 and 1,

while rectifiers I2 and I5 act in conjunction with,v

capacitors I3 and I4 to supply D. C. voltages between conductors 1 and 8 and conductors 1 and 9. plies an A. C. voltage to the tube 15, as1wil1 be more fully described subsequently.A Secondary.

winding I8 of transformer I1 supplies energy to transformer 22, the entire voltage4 ofgsecondary;

The secondaryof transformer 13 sup4 'accadde' the primary-'winding 2| of transformer 23. The

secondary 26 of transformer 23 will thereby be energized at ythis time.

Under these conditions, and prior' to the opf eration of 4initiating switch |45, the relay coil |39 is d'eenergizedfandjthe relay contacts which it controls 'arein the position shown in the drawing. The a'nodeof the added squeeze tube 32 is vdisconnected vfrom conductor!! by the open relay 'contact 31, and capacitor 43 is charged from secondary "winding 26 of transformer 23 by grid conduction 'ofy tube 32, the 'charge on 4capacitor 43 placingthe control 'grid '36' 'at `a voltage which, except Afor brief moments of grid conduction, is substantially negative toth'at of a cathode34.

The cathode v4'! of squeeze time tube '48 is at substantiallythe relatively high D. C. voltage' of conductor 8,"whi1ev the anode 49 'is negative with respect' to'the cathode 41 dueto the voltagedividhg'actiohof resistors 58 and 63. The 'c'olitrol 'g'lid 5| o'f tube is ngative to cathode 41 due'. tothe charge upon `calxacitor 51 which occurs by current'ow through resistor 38, the relay contact 56 and rectifier-44..

As' previously indicated, the transformer 13 supplies A. C. voltage between the anode and cathode of Weld timwtu'be 14, but this tube does not conductv due tothe negative voltage upon the control vgrid `11 thereof derived from the voltage dividing action of the serially connected resistors 18 and 1'9.

`Whenlthe` no Weld switch |03 is closed, the tube L94 'isconnected across` secondary winding 5 oftransformer. 4. The-shield grid y96 of tube 94 is substantially-at the cathode 93 voltage, while the controlgrid 92 `of tube 94 is negative with lrespectto the cathode 93 due to the voltage-dividing laction of resistors 88 and v9'|, thus preventing tube conduction.

The cathode r| I1 of hold time tube I| 4 and the control and shield grids |-3 and 8 respec` tively of tube I4 are at substantially the voltage of conductor 1. The anode ||6 is slightly positive with respect to the. cathode ||1 due to the charge upon capacitor |22 from the grid voltage network of tube |24 when the .repeat-nonrepeat switchl33 is in the repeat position indicated in thedrawing. Capacitor |2|^ is charged by the Volta'gefacross resistor 63.

rAs 1*previously- .indicated' there will be substantially no voltage across ffo time tube |24 when initiating :switch is open, Athe control -grid |23 being positive with respect to thecathode |26 by the'amount of charge upon capacitor |22.

A welding sequence is begun by closure of initiating switch |45 which deenergizes the transformer 23, voltage thereby appearingY across the terminals `of the secondary 24` of transformer 22. Tube |24 conducts `upon positive excursion of its anode/to 'enezgize relay coil |39 and to effect thereby operation of therelay contacts which it controls. Capacitor|4| is connected across the relay .coil to maintain it energized as previously described. The contacts of relay |39 are so -arrangedv that the normally closed` contacts will openbefore the normally open contacts close. Therefore, the energization of relay coil |39 will first elect vthe opening of relay Vcontacts 55 and 1|. The opening of the relaycontact 56 interrupts the 'fast charging'circuit to the capacitor 51,'the charge thereon being maintained however by'cura rent flow through rheostat 55 and resistor 54. Opening of relay contact 1| removes the short circuitzacross `capacitor yB9. Then "the normally open contacts close, closure-ofrela'y contact |411 effecting energization of the valve solenoidV |44 to initiate theapplication of pressurefto'the' weld'- j ing electrodes lll). Closure of relay contact 31 completes the circuit between the yanode 33 vof added squeeze tube 32 and the conductor '8.-

Closure of relay lcontact |42 establishes a holding circuit across the relay coil |39 so that, as "previously indicated, the relay rcoil will not be de-v energized should the'initiating 'switch |45 be Tin-'- advertent'ly opened 'during i a lwelding sequence.

Immediately 'uponthe deener'giz'ation of trans'- former l23, capacitor `43 beginsto discharge, to

initiate the 'squeeze delay timing, rat a rate deil terminedby the l'h'eost'at 42, control grid @Elapproaching the voltage of the'c'athode 34. fPosi'ti-'ve voltage pulsations, vbeing transmitted throughrectilierr 61, are 'synchronously transmitted to the shield 'grid v3 I of tube 32 which'willtherefore begin to conduct upon the occurrence of one ofwth'e'se synchronous pulsa-tions after capacitor 43 has suiiiciently discharged. At this time squeeze de-1 lay is ended, and squeeze time is started.

Conduction of tube 32 instantlyl drops the cathode 41 of tube'4`8 to a highly negative poten;

to conduct during one of thesesynchroni'zed .pub-4 sations. This conduction of tube 48'cau'sesrthe anode 49v thereof to drop in voltage 'due to current ilow through resistor 58. Thisfall in voltage of the anode 49 causes the cathodes of tubes 15 and '||4, the Weld time and .ho1d time tubes, to fall -to a substantially negative voltage with respect to the .anodes of the tubes. This voltage drop also causes the-shield grid 96 of tube 94` to swing substantially negative, this negative voltage being transmitted to the shield grid through the capacitor 98. Referring .first to the action at "weld time` tube 15',V the drop in voltage of the cathode A14 thereof causes a positive voltage to appearat the control grid 11 thereof.v

Tube 15 will therefore conduct upon the next positive swing of anode 16 voltage 'from the transformer 13, to energize the primary windings 8| and 82 of transformers 83 and 84. Theenergization oftransiormer -83 causes the secondary winding 85 thereof to pass current through rthe rectifier 86 to charge the capacitorl 81.- This charge causes a positive vvoltage `to appear upon the control grid 92 of the `tube 94, this v'voltage .be-- ing limited in amount bythe rectier-89. Tube 15 will continue to conduct and will therefore continue-'to maintain the energization -of trans formers 83 and 84, for a time determined bythe rate at. which the capacitor l69-is charged, this rate being determined'` by the Weld -timerheostat 68. As'will befseen :from the drawing, the capacitor 69 will begin Vto chargev 'asfsoon asy .tube '48 conducts. When the charge upon the 'capacitor 59 yhas been built up sufficiently, the cathode 14 of tube 15 Will become positive with respect to the-'control 'grid thereof, the tube 15 then. 'no longer conducting. When the 'rheostat vis 'set to eifect a minimum value, tube 15 will conduct for 'onlya half cycle.

The positive voltage upon `the vcontrol grid 92 of. tube 94 will .not cause @the tube 94 'to'conduct current until such time that a charge is huilt up upon the capacitor 98vwhich is sufficient to drive the shield grid 95 of tube 94 positive, this time being determined by the resistor 91. It should be noted that the capacitor 98 will be charged by a voltage having an A. C. ripple superimposed thereon so that the shield grid 98 is pulsatingly driven positive whereby tube 94 conduction will always occur at the beginning of a positive half cycle of voltage. The mechanical time lag in the operation of the relay contact |04 which is controlled by the relay coil 99 is such that weld current Iiow will be initiated at approximately the normal current zero of a weldingtransformer so that the welding current is initiated with a minimum transient. After the capacitor 98 has charged sufficiently, tube 94 will conduct at the synchronized instant aforementioned to energize the relay coil 99 and effect closure of the relay contact |04 in the igniter circuits of the back-to-back ignitron tubes |01 and |08 as previously indicated, at which time weld current flows. The closure of the relay contact |04 will, in conventional manner, eiiect current ilow through the associated igniters |05 and |06 to cause the electric discharge tubes |01 and |08 to conduct alternate half cycles of current flow through the welding transformer |09. The relay coil 99 is parallelled by capacitor |0| which will maintain the relay coil 99 energized during negative half cycles which follow a conducting half cycle of the tube 94.

Tube 94 will continue to conduct until such time, after the cessation of tube conduction, as, the charge upon the capacitor 81 in the control grid circuit of tube 94 has suiciently dissipated its charge so that the control grid is driven negatively to the voltage determined by the voltage-dividing resistors 88 and 9|. Upon termination of conduction of tube 94, the tuned elements comprising the capacitor |0| and the inductor |02 will, during the second half cycle following the last conducting half cycle through tube 94, effect a rapid deenergization of the relay coil 9| and drop out of the relay contact |04 to* prevent further weld current flow. As indicated in applicants copending application, Serial No. 148,190 filed March '1, 1950, for Electric Control Circuit, this drop-out will not occur at a 'time which would cause saturation of the welding transformer. It will therefore be seen that the tube 94, which conducts to effect operationof switch |04 and thereby cause weld current ilow, has been initiated after a predetermined delay and that this delay is independent of the operation of the solenoid valve. Weld of tube 48 the cathode l1 of the hold time" tube4 ||4 is driven substantially negative whereby a substantal positivev voltage appears upon the anode ||6 thereof. Tube |14 will not immediately conduct, however, due to the initial charge upon capacitor |2| which was established before operation of initiating switch |45. Upon the conduction of tube 15, and the energization of transformer `84 which results therefrom, and before capacitor |2| can discharge, the secondary windcapacitor |2| is dissipated through the hold time rheostat ||5 at a rate dependent upon its setting whereby tube ||4 will begin to conduct.- Tube ||4 conduction immediately charges ca pacitor |22, connected in the grid circuit of tube |24, in such a way that the tube |24 is immedl ately cut off. Cessation of current iiow through tube |24 deenergizes the relay coil |39 and returns the relay contacts controlled thereby to the position indicated in the drawing. As these relay contacts are operated, tubes 32, 48 and I4 are immediately cut oi, the cathodes of tubes 48 and ||4 returning to their initial positive voltages. The opening of relay contact |43 deenergizes the valve solenoid |44 to begin removal of air pressure fromthe electrodes. ing of relay contact 31 breaks the anodecircuit of tube 32; closure of relay contact 55 reestablishes the charging circuit for capacitor 51 which charges to prevent tube 48 conduction. Closure of relay contact 1| short circuits the timing capacitor 69 to remove the charge therefrom, and

opening of relay contact |42 returns control to the initiating contact |45.

If the repeat-nonrepeat switch |33 is `in the repeat position illustrated in the drawing, and' the initiating switch is held closed'upony termination of the welding sequence, off timing proceeds as capacitor |22 discharges through the rheostat |28 to remove the negative voltage upon the control grid |23 of tube |24 thereby permit` ting it to retire. The shield grid |21 of tube |24 is supplied with an A. C. voltage through resistor |35 which is of opposite polarityvto the anode voltage of tube |24 so that the tube |24 will begin to conduct only at the beginning of a positive half cycle of anode voltage, thereby ensur-`v ing synchronous initiation of a succeeding weld sequence. Relay coil |39 will thereby be reenergized, and the contacts controlled thereby will be operated. The reclosure of relay contact 31:

Will cause immediate conduction of the squeeze delay tube 36 in the subsequent weld sequence,

due to the fact that transformer 23 had been' deenergized since the initial closure of the initiating contact |45 at the beginning of the control weld sequence, and the capacitor 43, theref fore, has no charge thereon. At the minimumr timing setting of the rheostat 55, squeeze timeV tube 48 will immediately conduct upon'the con-Y duction of squeeze delay tube 32 so that in these subsequent weld sequences the actual period between the initation of pressure and theVv now of weld current is shorter than was the The operation of the circuit upon conduction of tubef similar period of the iirst weld sequence.

49 is then as has been previously described.

Ii the switch |33 is in the non-repeat position, A. C. anode voltage will be applied to the shield grid |21 of the tube |24 through the capacitor |38, current from the shield grid maintaining a negative charge upon the capacitor |224 -to prevent it from timing out and to thereby.1 maintain vthe tube |24 in its cut-oir position.'1 Tube |24 will not ,conduct until the initiating. switch |45 is opened to eliminate the voltage of', the secondary. winding 24 of transformer 22.I

thereby eliminating the charging circuit for the capacitor |22 Vthrough the shield grid |24, Whereby the charge upon capacitor |22 will quickly The open-v 1- dissipatetcpermit .tube |24 to again-conduct uponreclosure; of initiating 'switchl i 45.

It will be seen that the circuit arrangement of the present invention provides afweld sequencing control in which initiation of ythe hold time period is independent of weld current flow, so that the hold time period may be initiated before weld current flows, permitting ineffect, a negative hold time if such be necessary to effect synchronism between the ow of weld current and electrode pressure. Furthermore, as previously described, the length of the period between the application of pressure to the welding electrodes and the flow of weld current will be longer in the first Welding sequence than in subsequent'welding sequences which occur without the initiating switch being opened. It will, therefore, be seen that this combination of features permits welds, in circuits using fluid pressure for effecting electrode pressure, to be made with great rapidity, the timing elements being readily adjustable so that weld current will ow only when substantial pressure is exerted by the welding electrodes, regardless of the inertial effects of the welding electrodes and the pressure system associated therewith.

What is claimed is:

1. In a timing circuit, an electronic tube having a pair of principal electrodes and a control electrode, a capacitor, means connecting one terminal of said capacitor to said control electrode, means for charging said capacitor, means for initiating a timing period, means for electrically connecting one of said principal electrodes to the other terminal of said capacitor upon operation of said initiating means, means for changing the potential of said one of said principal electrodes upon operation of said initiating means, and means for adjustably discharging said capacitor whereby the voltage of said control electrode will gradually approach that of said one of said principal electrodes after operation of said initiating means.

2. In a timing circuit, means for initiating a timing period, a first electronic tube, a second electronic tube, means for initiating the conduction of said first electronic tube upon operation of said initiating means, means for initiating conduction of said second electronic tube a rst predetermined time after the operation of said first electronic tube, adjustable timing meansfor terl minating the conduction of said first electronic tube, means for terminating the 'conduction of said second electronic tube a second predetermined time after the termination` of conduction of said first electronic tube, and means `operated by said second electronic tube for effecting a control function.

3. In a welding device including electrodes movable relatively by fluid pressure, initiating means, first means operable upon operation of said initiating means for eiecting the application of pressure to said electrodes, a first electronic tube, timing means for effecting the conduction of said first electronic tube an adjustable time after operation of said rst means, a second electronic tube rendered conductive by conduction of said first electronic tube, means for interrupting the conduction of said second tube, a third electronic tube, means for effecting conduction of said third tube a predetermined time after conduction of said rst tube, means for stopping conduction cf said third tube a predetermined time after cessation of conduction of said second tube, means responsive to conduction of said third tube for effecting load current flow, and means controlled by said second tubefor interrupting the operation of said first means an adjustable .time after cessation of conduction of said second tube whereby .the removal of pressurefrom the electrodes. may be started before the interruption of load current ow.

4. The device as claimed in claim 3 in which said timing means for effecting the conduction of said rst electronic tube an adjustable time after operation of said initiating means includes an additional electronic tube and means for connecting said additional electronic tube and said rst electronic tube in series whereby said first electronic tube may conduct only during the conduction of said additional electronic tube.

5. The device as claimed in claim 3 in which said timing means for effecting the conduction of said rst electronic tube an adjustable time after operation of said initiating means includes an additional electronic tube and means for connecting said -additional electronic tube and said first electronic tube in series, adjustable means for preventing the conduction of said additional electronic tube until a predetermined time after the operation of said initiating means, and adjustable means for preventing the conduction of said first electronic tube until a predetermined time following the conduction of said additional electronic tube.

6. The device as claimed in claim 3 in which said timing means for effecting the conduction of said rst electronic tube an adjustable time after operation of said initiating means includes an additional electronic tube and means for connecting said additional electronic tube and said rst electronic tube in series, adjustable means for preventing the conduction of said additional electronic tube until a predetermined time after the operation of said initiating means, and adjustable means for preventing the conduction of said first electronic tube until a predetermined time following the conduction of said addition-al electronic tube, said adjustable means for preventing the conduction of said additional tube for a predetermined period including means disabled by operation of said initiating means whereby the conduction of said additional tube is delayed only once during any single period of operation of said initiating means.

2. The device as claimed in claim 3 in which timing means for effecting the conduction of said first electronic tube an adjustable time after operation of said initiating means includes an additional electronic tube and means for connecting said additional electronic tube and said rst electronic tube in series, adjustable means for preventing the conduction of said additional electronic tube until a predetermined time after the operation of said initiating means, and adjustable means for preventing the conduction of said first electronic tube until a predetermined time following the conduction of said additional electronic tube, said adjustable means for preventing the conduction of said additional tube .for a predetermined period including a transformer and a capacitor charged thereby, opertion of said initiating means shorting out said transformer whereby the conduction of said additional tube is delayed only once during any single period of operation of said initiating means.

8. The device as claimed in claim 3 in which said means for effecting conduction of said third tube a predetermined time after conduction of said first tube includes means responsive to ccnduction of said second tube.

9. The device as claimed in claim 3 in which said third tube has a pair of principal electrodes and a pair of control electrodes, said means for effecting conduction of said third tube including a first capacitor connected to one of said control electrodes charged subsequent to conduction of said rst tube, and a second capacitor charged by conduction of said second tube connected to the other of said control electrodes.

10. The device as claimed in claim 3 in which said means controlled by said second tube for interrupting the operation of said first means includes a fourth electronic tube having a pair of principal electrodes and a control electrode, a transformer, means connecting the primary of said transformer in series with said second tube, a capacitor, means connecting said capasitor to vsaid control electrode, means connecting the secondary of said transformerv to said capacitor, and means for adjustably discharging said capacitor upon cessation of conduction of said. second tube and consequent deenergization of said transformer.

ERNEST G. ANGER.Y

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

